Texas A&M quarterback Johnny Manziel, a top candidate for the Heisman Trophy, has injured his left knee in tonight's game against Missouri.

Manziel grabbed the knee, which twisted awkwardly as he was being tackled. After grimacing in pain while clutching his knee, Manziel walked gingerly off the field and sat down on a bench on the sideline.

Texas A&M quarterback Johnny Manziel sustained a knee injury in the first quarter of the Aggies' game against Missouri. He left the game, but did return. (AP Photo)

Trainers asked him about a knee brace, but he eventually left the sideline to be treated in the locker room. He returned to the game, but did so only after testing his knee with a couple of short runs on the sideline.